This invention relates to a transport system by which semi-conductor wafers can be carried from station to station for processing into integrated circuits. Circular, semi-conductor wafers up to six inches in diameter but only 15-20 thousandths of an inch thick are common in the semi-conductor industry. A non-conductive base, such as silicon, is coated with a metallic conductive material to form the semi-conductor wafers. After these wafers are coated and baked they are typically sent to a photoresist area where photographically reduced circuitry is imprinted upon the wafers by a process of photo reduction, masking, etching, and processing. A multitude of extremely small and complex circuits are etched out of the conductive layer on the semi-conductor material. After leaving the photoresist area the semi-conductive wafer may be transported to a dry process area and subsequently onto a pre-diffusioned cleaning area, or back to the photoresist area to have a second circuit overlayed onto the first. Alternately, after the photoresist, the semi-conductor wafer may go to an ion implant area where ion impurities are forced into the conductive material; from the implant area the wafer is sent onto either the pre-diffusion clean area or back to the dry process area. Semi-conductive wafers leaving the pre-diffusion clean area pass either through a metals area or onto a furnace load station wherein the semi-conductor materials are heated to an elevated temperature in order to finish the processing step.
Since the circuitry printed on the semi-conductor wafers is extremely small, it only takes a small sized particle to either short circuit the imprinted circuitry or alternately, to block processing chemicals from reaching every portion of the circuitry imprinted on the semi-conductor wafer. It is thus essential that even tiny contaminants be kept out of the semi-conductor processing areas.
Several of the separate processing areas, such as the furnace or the ion implant area operate in a controlled environment. There is a danger of contamination, however, when the wafers are transported from one processing area to the next, or when the wafers travel within a processing area which does not have a controlled environment.
Some of the present systems to prevent contamination consist merely in enclosing the wafers in a closed box during transportation. Such an enclosure does not prevent contamination from the airborne particulates entrapped within the box.
Accordingly, one object of this invention is to provide an improved transport system whereby semi-conductor wafers can be transferred from one processing area to the next with minimal risks of contamination.
Another object of this invention is to provide an improved transport system whereby semi-conductor wafers can be transferred within a single processing area when the processing area does not have a controlled, particulate-free environment.
Since the wafers are extremely thin and the circuitry printed upon them is even thinner, the danger of abrasion, scratches, and even breakage of the wafer cannot be ignored. Every time the wafer is physically handled, or subjected to a shock the chances of contamination and damage are increased.
Early transport techniques included manually carrying the wafers either individually or in boxes from the processing area to the next. The batch transportation of a number of wafers in a single carrier further opens the entire batch of wafers to contamination or damage from shock loads since the chances are that one wafer will be subjected to the same contaminant or shock load as the adjacent wafers.
Early attempts to automate the transport process by the use of conveyor belts and platens or by air or vibratory tracks did not solve either the contamination of the abrasion problem. The conveyor systems subjected the wafers to numerous vibratory loads. The air transport systems increased the risk of contamination through the very air used to transport the wafers. Vibratory tracks increased the abrasion of the wafers and platen conveyor systems subjected the wafers to numerous vibrations as they rolled over each platen, thereby increasing the chances of abrasion and increasing the shock loads tending to fracture the wafers.
Accordingly, a still further ojbect of this invention is to provide an automated transport system which minimizes the manual handling of the semi-conductor wafers or of the carriers, thereby minimizing the chances of contamination or the possibility of scratching or breaking the fragile wafers.